This invention relates to a dash pot basket for a heat exchanger tube cleaning element.
It is known from the above-identified patents to connect individual elongated cleaning element capturing cages or baskets to both ends of longitudinally extending tubes disposed in a heat exchanger housing. The tube ends are held in position at both ends by transverse tube sheets. The baskets are adapted to contain shuttleable cleaning elements such as brushes. Fluid flowing in one direction through the tubes keeps the cleaning elements captured within their respective basket chambers, while the fluid discharges outwardly through slot-like openings in the basket walls. Upon reversal of fluid flow, the cleaning elements are forced out of their baskets and through the tubes to the baskets at the opposite tube ends to thereby perform a tube cleaning action.
In many installations, as where heat exchanger temperatures and pressures are relatively low, tube cleaning shuttle brushes have often been made of plastic. However, in high temperature-high pressure applications, the brushes are preferably made of metal. The metal brushes have comprised an elongated wire twist stem having a fine bristle wire looped through the twist along the stem length. End caps are secured to the stem ends. The stem, bristles and end caps may be made of carbon steel, stainless steel or the like.
In many instances, the brush bristles have been held in position by friction within the twisted stem. However, it has been noted that the bristles have tended to loosen over a period of time, requiring brush replacement. Considering the many hundreds of tube cleaning brushes installed in a heat exchanger, brush replacement becomes costly and time consuming.
It has been discovered that one of the causes of brush bristle loosening is the shock which has occurred when the brush cap forcefully engages the stop member at the end of the basket. The shock force is in an axial direction and, over a period of time wherein many such shocks occur, it has been found that the brush twist wire tends to open, thereby permitting the bristles to come loose.
It is a task of the present invention to substantially reduce or eliminate the loosening of brush bristles form their anchor. It is a further task to prevent the twist wire stem from opening or distorting during the shuttling operation. It is yet another task to substantially reduce or eliminate the shock forces on the brush when it has reached the end of its travel in the basket.
In accordance with the various aspects of the invention, the brush capturing element or basket is provided with a dash pot at its outer end which not only serves as a brush stop but which also creates a hydraulic cushion to slowly decelerate the brush before it engages the stop. The dash pot provides a recess for receipt of a brush end cap. In the present embodiment, the I.D. of the recess is only slightly larger than the diameter of the brush end cap to thereby create a circumferential restricted flow passage for fluid to escape from the recess into the basket as the cap enters the recess. The I.D. of the recess may be slightly less than that of the heat exchanger tubes, while the I.D. of the basket walls may be somewhat greater.